1. Field
Certain embodiments of the invention relate generally to communication systems, and more particularly, to cellular communication systems that utilize radio access technologies (RATs), such as Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), and Third Generation Partnership Project (3GPP) Long-Term Evolution (LTE).
2. Description of the Related Art
Cellular communication systems utilize radio frequencies for the transmission and reception of its signals. A band is a plurality of radio frequencies, in which channels are generally used for the transmission and reception of signals. A channel can include a single radio frequency or a plurality of radio frequencies.
In a shared band operation, a specific band can be divided between different users or operators of the cellular communication system. Shared band operation can include licensed shared band operation or unlicensed shared band operation. In licensed shared band operation, one or more operators can purchase a specific portion of an available radio spectrum for transmission and reception of cellular signals. A radio spectrum is a portion of an electromagnetic spectrum corresponding to radio frequencies. A purchased portion of the radio spectrum is also referred to as a licensed band. The licensed band is shared between the one or more operators. The sharing of the licensed band can enable operators to deploy local access points on the licensed shared band. An example of a local access point is a femtocell, which is a small cellular base station. The sharing of the licensed band can also enable operators to allow device-to-device communication between two or more communication devices on the licensed shared band. The sharing of the licensed band can also be controlled by a central operator, or a plurality of operators can agree that the licensed band is to be shared and that access is to be contended by the plurality of operators.
In unlicensed shared band operation, the band is not owned by any operator and is referred to as an unlicensed band. The unlicensed band can be utilized by any system, and thus, is referred to as an unlicensed shared band. Some unlicensed shared bands, while not owned by any operator, are regulated, and the communication devices on those unlicensed shared bands must still follow regulations. Example radio technologies operating on unlicensed shared bands include wireless local area networks (WLAN), Bluetooth (BT) networks, and Zigbee networks. Due to the fact that an unlicensed shared band is available and for use by any communication device, the interference environment can be unpredictable. This can mean that predetermined quality of service (QoS) cannot be guaranteed.
Communication on an unlicensed shared band is generally based on sharing an available channel between different communication devices. The different communication devices may utilize a common RAT, but in certain scenarios, the different communication devices may utilize different RATs. In an unlicensed shared band, channel access can be distributed, where communication devices can detect a channel, and utilize a channel reservation scheme known to other communication devices in order to reserve a right to access the channel. In distributed channel access, a transmitting communication device and a receiving communication device are generally not synchronized to a global reference. Thus, in the beginning of each transmitted packet, a common sequence can be transmitted by the transmitting communication device in order to allow the receiving communication device to synchronize itself with, and lock on to, the transmission.
Transmissions on an unlicensed shared band, that do not utilize a common timing reference shared by the transmitting communication device and the receiving communication device, are generally short in duration in order to allow multiple communication devices to share the channel. Generally, in this scenario, a transmitting communication device only transmits a few packets at a time before the transmitting communication device defers its access to another transmitting communication device that also occupies the channel. After a random duration (which can depend on the number of communication devices sharing the channel), the transmitting communication device transmits again. Therefore, specific measures are required in order to initially synchronize the transmitting communication device and receiving communication device in the beginning of each data transmission by synchronizing the receiving communication device with the data transmission (i.e., informing the receiving communication device when the first packet of the data transmission begins). In addition to synchronization, the transmitting communication device can indicate frequency resources that can be utilized for transmission. In general, a transmitting communication device may only utilize a portion of the frequency resources, and can indicate to the receiving communication device which portion of the frequency resources the transmitting communication device will utilize for transmission.